This invention relates to a rotary head recording/reproducing apparatus for recording digital signals onto helical tracks on a tape-like recording medium and reproducing the digital signals therefrom with a rotary head rotating at a predetermined speed.
There has been known a rotary head recording/reproducing apparatus for recording/reproducing digital audio data, digital video data or analog video data with a rotary head onto/from a magnetic tape guided to run by cylindrical surface of the rotary drum.
In recording, the rotary head recording/reproducing apparatus records data onto a magnetic tape having no guard band, as shown in FIG. 1, with a recording magnetic head (hereinafter referred to as the recording head). That is, in this rotary head recording/reproducing apparatus, when the recording head helically scans the magnetic tape to repeatedly form tracks Ta and Tb having an inclination .alpha. for recording data, an azimuth angle of +.theta. in relation to the direction M perpendicular to the running direction L of the magnetic head is provided in the track Ta and an azimuth angle of -.theta. in relation to the direction M is provided in the track Tb. Thus, crosstalk between adjacent tracks is reduced.
It has been known that, in such azimuth recording, reproduction is carried out by using a reproducing magnetic head (hereinafter referred to as the reproducing head) to check whether data has been correctly recorded during one turn of the rotary drum. Such combination of recording with reproduction is called read-after-write (RAW). The rotary head recording/reproducing apparatus carries out RAW during one turn of the rotary drum.
An exemplary rotary head recording/reproducing apparatus for carrying out RAW during one turn of the rotary drum as described above has a rotary drum D in which recording heads H.sub.W1, H.sub.W2 are provided at 180.degree. to face each other and in which reproducing heads H.sub.R1, H.sub.R2 are provided at 180.degree. to face each other, as shown in FIG. 2. The recording head H.sub.W1 and the reproducing head H.sub.R1 are located at 90.degree.. That is, in this rotary head recording/reproducing apparatus, the recording head H.sub.W1, reproducing head H.sub.R1, recording head H.sub.W2 and reproducing head H.sub.R2 are located on the rotary drum in this order each at an angle of 90.degree.. In this rotary head recording/reproducing apparatus, a magnetic tape t is lapped about the rotary drum D at a lap angle of approximately 90.degree..
Another exemplary rotary head recording/reproducing apparatus for carrying out RAW during one turn of the rotary drum has a rotary drum D in which recording heads H.sub.W1, H.sub.W2 and reproducing heads H.sub.R1, H.sub.R2 are provided at an angle of 180.degree., as shown in FIG. 3. In this rotary head recording/reproducing apparatus, a magnetic tape t is lapped about the rotary drum D at a lap angle of approximately 180.degree..
In the rotary head recording/reproducing apparatus as shown in FIG. 3, the recording heads H.sub.W1, H.sub.W2 are integrally formed to have a double-azimuth structure with an extremely small gap between the two heads. The reproducing heads H.sub.R1, H.sub.R2 similarly form the double-azimuth structure. In addition, the azimuth angle of the closely provided heads differs to reduce crosstalk between adjacent tracks, as explained with reference to FIG. 1.
In both apparatuses shown in FIGS. 2 and 3, the magnetic tape t is fed at a constant speed by a capstan C and a pinch roller P, in the direction from a supply reel Rs to a takeup reel Rt (as indicated by an arrow N). The rotary drum D rotates in the direction indicated by an arrow O.
In the rotary head recording/reproducing apparatus as shown in FIG. 2, the reproduction heads H.sub.R1, H.sub.R2 do not carry out reproduction while the recording heads H.sub.W1, H.sub.W2 are carrying out recording. Therefore, reproduction is carried out when the recording heads H.sub.W1, H.sub.W2 do not operate, so that reproduction for checking in RAW can be carried out without causing any crosstalk from the recording system to the reproduction system.
Also in the apparatus as shown in FIG. 3, the reproducing heads H.sub.R1, H.sub.R2 do not carry out reproduction while the recording heads H.sub.W1, H.sub.W2 are carrying out recording. Therefore, reproduction is carried out when the recording heads H.sub.W1, H.sub.W2 do not operate, so that reproduction for checking in RAW can be carried out without causing any crosstalk from the recording system to the reproduction system.
With these rotary head recording/reproducing apparatuses, high-speed search can be realized by reading a search signal recorded on the track of the magnetic tape. Particularly, in the rotary head recording/reproducing apparatus, head search or search is carried out using a start ID, a program number and a time code as search signals. For example, though where the start ID indicating start of a program is recorded cannot be predicted during reproduction, the start ID can be securely read even in high-speed search in the rotary head recording/ reproducing apparatus.
Meanwhile, in the above-described high-speed search, the reproducing head helically transverses the recording track. Therefore, in the rotary head recording/reproducing apparatus as shown in FIG. 2, since the reproducing head H.sub.R1 or the reproducing head H.sub.R2 intermittently contacts the magnetic tape, as shown in FIG. 4, an area in which search signals cannot be read may be generated. That is, an area A.sub.0 in which search signals cannot be read at all is generated between a readout area A.sub.R1 corresponding to a locus X.sub.R1 traced by the reproducing head H.sub.R1 on the magnetic tape t and a readout area A.sub.R2 corresponding to a locus X.sub.R2 traced by the reproducing head H.sub.R2. Thus, high-speed search is difficult unless search signals are recorded in the area of A.sub.R1 +A.sub.0.
Also, it is assumed that high-speed search at centuple speed is carried out in the rotary head recording/reproducing apparatus as shown in FIG. 3. In this case, the loci of the reproducing head H.sub.R1 and the reproducing head H.sub.R2 are indicated by X.sub.R1 and X.sub.R2, respectively, as shown in FIG. 5. Accordingly, the same search signal must be recorded in 200 or more tracks so that the search signal can be detected at a high speed.
As the search signal must be recorded in a number of tracks for realizing high-speed search, a recording area for main signals is reduced, disturbing improvement of recording density.
The rotation speed of the rotary drum D differs between cases of FIG. 2 and FIG. 3, with rotary drum D of FIG. 3 rotating at a higher speed.
Thus, plural reproducing heads need be provided at an equal distance on the rotary drum to efficiently read out the search signal recorded on tracks of the magnetic tape in high-speed search. However, as is described above, providing plural reproducing heads at an equal distance has limitation in consideration of crosstalk in RAW.